The invention concerns a filtering apparatus for the industrial, discontinuous separation of solids from liquids and in which the filter cake is removed automatically. The apparatus includes a housing, a filtering element support which is mounted within the housing and has a filtering element, an inlet opening for the suspension to be filtered, a discharge opening for the filtrate, and a device for removing the filter cake which comprises at least one screw conveyor. The screw conveyor, which may be a cut-flight screw conveyor, a spiral screw conveyor or a ribbon screw conveyor for instance, conveys the filter cake which accumulates on the filtering element towards the cake removal opening in the center of the housing floor. A hollow shaft which can be raised and lowered is mounted coaxially with the vertical main axis of the filtering apparatus. The upper end of the hollow shaft is rigidly fixed to a drive and the lower end to the screw conveyor or conveyors and the drive shaft for the conveyor members is mounted within this hollow shaft. The lower end of the drive shaft is coupled to the conveyor members via a bevel gear.
The types of filtering apparatus of this kind hitherto known in the art have several shortcomings some of which are briefly outlined below.
As soon as the filter cake reaches a certain state of dryness, cracks which penetrate down to the filter form over the whole of its surface. On account of these cracks the vacuum or pressure is impaired and the rate of filtration falls. These cracks must be continuously smoothed out in order to keep the filtration time of open suction filters within economic limits. This is naturally a laborious and time-consuming procedure.
Another significant disadvantage of known filtering apparatus of this kind is that although efficient conveyor members are present to remove the filter cake, the removal opening however is to a large extent obstructed by elements, for instance those holding the removal pipe. The situation is not conducive to the rapid removal of the filter cake.
It is also impossible with conventional filtering apparatus to break up the solid cake into small pieces quickly and thoroughly after the first filtration and then to wash it. With many products, however, it is essential to wash the solid cake once or several times.